The invention relates to an adaptor for auto strobo units, and more particularly, to an adaptor which is used to couple an internal electrical circuit of a camera with the electrical circuit of an auto strobo unit.
As is well recognized, an auto strobo unit comprises a photometric control circuit which produces an illumination interrupt signal when the flashlight illumination reaches an optimum value for an object being photographed, thus automatically stopping the illumination. Various forms of auto strobo units are known including one having a photometric control circuit which comprises a light receiving element, another having no photometric control circuit but having an illumination interrupt terminal to which an illumination interrupt signal may be externally applied or a further version which includes both the photometric control circuit and the illumination interrupt terminal adapted to be connected with an external circuit.
An auto strobo unit having an illumination interrupt terminal, is combined with a camera of the type in which the exposure is automatically controlled, so that an illumination interrupt signal is derived from a photometric control circuit contained within the camera and is applied to the illumination interrupt terminal. Hence, an auto strobo unit having only the illumination interrupt terminal cannot properly function as an auto strobo unit unless it is coupled with such an automatic exposure controlled camera.
An auto strobo unit having an illumination interrupt terminal is designed to have an illumination interrupt signal of positive polarity applied to said terminal. This signal inhibits the interruption of the illumination in response to the application of a signal of a negative polarity. This is because various makers employ a design scheme, sometimes referred to as a system or systematized camera, in which accessories associated with a particular camera are specially designed to suit it. However, recently, a combination of a camera and an auto strobo unit has been offered in which an illumination interrupt signal of a negative polarity is derived from a system camera and applied to the illumination interrupt terminal of the unit. However, this auto strobo unit cannot be coupled with a camera of the type which produces an illumination interrupt signal of a positive polarity. Conversely, a camera which produces an illumination interrupt signal of a negative polarity cannot be coupled with an auto strobo unit having an illumination interrupt terminal which is designed to receive a signal of a positive polarity.
In a combination of a systematized camera and an auto strobo unit, an illumination interrupt signal which is derived from a photometric control circuit including a light receiving element is of a low magnitude and hence is amplified to a given level either within the camera or in the strobo unit. This presents no problem whatsoever in a systematized combination. However, when the combination includes a camera which is not of the systematized type, the magnitude of the output voltage is insufficient to provide a satisfactory operation even though the signal has the proper polarity. In other words, the combination will not operate if the amplification feature is not provided in either the strobo unit or the camera. As a result, the conventional auto strobo unit failed to enjoy an interchangeability and a universal acceptance in the art because of the systematized limitation even though it has an effective light conditioning feature.